The present exemplary embodiment relates to a method of controlling the width of a gap in an optical element. It finds particular application in conjunction with control of a waveguide gap width for minimizing optical transmission loss, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Optical communication components, which use light waves and beams to carry information, are widely used in the telecommunications industry. Many optical components employ waveguides to convey the optical signals. The fabrication of waveguides in silica typically includes forming a core layer, which is primarily SiO2 doped with another material, such as Ge or TiO2. A cladding layer is formed on the core layer, such as SiO2, doped with another material, such as B2O3 and/or P2O5, in which the waveguides are formed. A trench is etched through the waveguide and into the silicon substrate.
Processing technologies for forming micro-electromechanical system (MEMS) devices include bulk micromachining of single crystal silicon and surface micromachining of polycrystalline silicon. Bulk micromachining of single crystal silicon typically utilizes wet anisotropic wet etching. The etch rate can be modified by the incorporation of dopant atoms, such as boron, which substitute for silicon atoms in the crystal lattice. Deep Reactive Ion Etching (DRIE) utilizes sidewall passivation and ion beam directionality to achieve etch anisotropy. Surface micromachining of polycrystalline silicon typically utilizes chemical vapor deposition (CVD) and reactive ion etching (RIE) patterning techniques to form mechanical elements from stacked layers of thin films Commonly, CVD polysilicon is used to form the mechanical elements, CVD nitride is used to form electrical insulators, and CVD oxide is used as a sacrificial layer. Removal of the oxide by wet or dry etching releases the polysilicon thin film structures.
Optical switches are examples of MEMS devices and are used in optical fiber transmission networks to route optical signals along various signal paths. A MEMS shuttle switch employs two waveguide gaps while a cantilever switch uses one gap. A light signal traveling down one stationary waveguide is transmitted into another stationary waveguide via the gap. Switches of this type are disclosed, for example, in U.S. Pat. Nos. 5,578,976 to Yao; 5,619,061 to Goldsmith et al.; 5,638,946 to Zavracky; and 6,229,683 to Goodwin-Johansson, which are incorporated herein by reference in their entireties. These switches are typically configured as a cantilever or suspended mass structure and have a switch contact that moves in a generally perpendicular direction with respect to the plane of the substrate on which the device is fabricated or laterally thereto.
Waveguide gaps are generally filled with air, although other optical media have been employed. U.S. Pat. No. 6,744,951 to Dawes, for example, discloses a method of coupling optical waveguides separated by a gap of about 2–500 μm which includes filling the gap with a photo-polymerizable composition and curing the composition with photo-radiation passing through the waveguides.
Destructive interference due to the formation of a Fabry-Perot cavity may occur within an optically transparent medium such as a waveguide gap. The destructive interference attenuates the laser energy flux through the optically transparent medium. Optical losses due to the waveguide gaps in such devices may make a significant contribution of the overall transmission loss of the system.